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Date: Wed, 06 Jan 2010 14:21:07 -0500
From: Trond Myklebust <Trond.Myklebust@...app.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
Steve Rago <sar@...-labs.com>,
"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"jens.axboe" <jens.axboe@...cle.com>,
Peter Staubach <staubach@...hat.com>,
Arjan van de Ven <arjan@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] improve the performance of large sequential write NFS
workloads
On Wed, 2010-01-06 at 20:07 +0100, Peter Zijlstra wrote:
> On Wed, 2010-01-06 at 13:52 -0500, Trond Myklebust wrote:
> > On Wed, 2010-01-06 at 19:37 +0100, Peter Zijlstra wrote:
> > > On Wed, 2010-01-06 at 13:26 -0500, Trond Myklebust wrote:
> > > > OK. It looks as if the only key to finding out how many unstable writes
> > > > we have is to use global_page_state(NR_UNSTABLE_NFS), so we can't
> > > > specifically target our own backing-dev.
> > >
> > > Would be a simple matter of splitting BDI_UNSTABLE out from
> > > BDI_RECLAIMABLE, no?
> > >
> > > Something like
> >
> > OK. How about if we also add in a bdi->capabilities flag to tell that we
> > might have BDI_UNSTABLE? That would allow us to avoid the potentially
> > expensive extra calls to bdi_stat() and bdi_stat_sum() for the non-nfs
> > case?
>
> The bdi_stat_sum() in the error limit is basically the only such
> expensive op, but I suspect we might hit that more than enough. So sure
> that sounds like a plan.
>
This should apply on top of your patch....
Cheers
Trond
------------------------------------------------------------------------------------------------
VM: Don't call bdi_stat(BDI_UNSTABLE) on non-nfs backing-devices
From: Trond Myklebust <Trond.Myklebust@...app.com>
Speeds up the accounting in balance_dirty_pages() for non-nfs devices.
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
---
fs/nfs/client.c | 1 +
include/linux/backing-dev.h | 6 ++++++
mm/page-writeback.c | 16 +++++++++++-----
3 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index ee77713..d0b060a 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -890,6 +890,7 @@ static void nfs_server_set_fsinfo(struct nfs_server *server, struct nfs_fsinfo *
server->backing_dev_info.name = "nfs";
server->backing_dev_info.ra_pages = server->rpages * NFS_MAX_READAHEAD;
+ server->backing_dev_info.capabilities |= BDI_CAP_ACCT_UNSTABLE;
if (server->wsize > max_rpc_payload)
server->wsize = max_rpc_payload;
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 42c3e2a..8b45166 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -232,6 +232,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
#define BDI_CAP_EXEC_MAP 0x00000040
#define BDI_CAP_NO_ACCT_WB 0x00000080
#define BDI_CAP_SWAP_BACKED 0x00000100
+#define BDI_CAP_ACCT_UNSTABLE 0x00000200
#define BDI_CAP_VMFLAGS \
(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
@@ -311,6 +312,11 @@ static inline bool bdi_cap_flush_forker(struct backing_dev_info *bdi)
return bdi == &default_backing_dev_info;
}
+static inline bool bdi_cap_account_unstable(struct backing_dev_info *bdi)
+{
+ return bdi->capabilities & BDI_CAP_ACCT_UNSTABLE;
+}
+
static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
{
return bdi_cap_writeback_dirty(mapping->backing_dev_info);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index aa26b0f..d90a0db 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -273,8 +273,9 @@ static void clip_bdi_dirty_limit(struct backing_dev_info *bdi,
avail_dirty = 0;
avail_dirty += bdi_stat(bdi, BDI_DIRTY) +
- bdi_stat(bdi, BDI_UNSTABLE) +
bdi_stat(bdi, BDI_WRITEBACK);
+ if (bdi_cap_account_unstable(bdi))
+ avail_dirty += bdi_stat(bdi, BDI_UNSTABLE);
*pbdi_dirty = min(*pbdi_dirty, avail_dirty);
}
@@ -512,8 +513,9 @@ static void balance_dirty_pages(struct address_space *mapping,
nr_unstable_nfs;
nr_writeback = global_page_state(NR_WRITEBACK);
- bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY) +
- bdi_stat(bdi, BDI_UNSTABLE);
+ bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY);
+ if (bdi_cap_account_unstable(bdi))
+ bdi_nr_reclaimable += bdi_stat(bdi, BDI_UNSTABLE);
bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
@@ -563,11 +565,15 @@ static void balance_dirty_pages(struct address_space *mapping,
* deltas.
*/
if (bdi_thresh < 2*bdi_stat_error(bdi)) {
- bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_DIRTY) +
+ bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_DIRTY);
+ if (bdi_cap_account_unstable(bdi))
+ bdi_nr_reclaimable +=
bdi_stat_sum(bdi, BDI_UNSTABLE);
bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
} else if (bdi_nr_reclaimable) {
- bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY) +
+ bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY);
+ if (bdi_cap_account_unstable(bdi))
+ bdi_nr_reclaimable +=
bdi_stat(bdi, BDI_UNSTABLE);
bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
}
--
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